USCG Exam PracticeMotor controllers and remote control
In an ungrounded three-phase AC system aboard a vessel, how many motor-running protective devices (overload coil or heater type relay) are required per 46 CFR §111.70-1, and where must they be placed?
- ✓ Two devices, placed in any two ungrounded conductorsCorrect
- B. Three devices, one in each ungrounded conductor
- C. Two devices, placed in the two grounded conductors
- D. One device, placed in the highest-current ungrounded conductor
Why A is correct
46 CFR §111.70-1(b) states that in ungrounded three-phase AC systems, only two motor-running protective devices need be used, placed in any two ungrounded conductors. The exception applies when a wye-delta or delta-wye transformer is used.
Cited:46 CFR §111.70-1